Mobile communication systems were developed to provide the subscribers with voice communication services on the move. With the rapid advance of technologies, the mobile communication systems have evolved to support high speed data communication services beyond the early voice-oriented services. However, the limited resource and user requirements for higher speed services in the current mobile communication system spur the evolution to more advanced mobile communication systems.
Meanwhile, the mobile communication systems adopt traffic adaptation techniques to adjust the system communication resource dynamically according to the change of the required traffic amount to process the traffic efficiently. In the case of the Long Term Evolution (LTE) system of the 3rd Generation Partnership Project (3GPP) as an asynchronous mobile communication standardization organization, the numbers of downlink and uplink subframes are configured at various ratios in a radio frame in Time Division Duplex (TDD) mode. This configuration is called uplink/downlink configuration, and the numbers of the downlink and uplink subframes in one radio frame change depending on the uplink/downlink configuration. The LTE TDD system uses the traffic adaptation technique of selecting/adopting the uplink/downlink configuration dynamically depending on the change of the required downlink and uplink traffic amounts so as to use the radio communication resource efficiently, resulting in improvement of throughput.
FIG. 1 is a diagram illustrating an exemplary traffic adaptation technique based on a plurality of uplink/downlink configurations in the LTE TDD system.
In this example, it is assumed that the system performs traffic adaptation with three Uplink/Downlink (UL/DL) configurations. Assuming that the three UL/DL configurations are UL/DL conf#0 100, UL-DL conf#1 101, and UL/DL conf#2; the UL/DL configurations have different UL/DL subframe ratio in the radio frame spanning 10 ms. Here, a subframe spans 1 ms.
For example, the UL-DL conf#0 100 consists of 2 DL subframes (D), 2 special subframe (S), and 6 UL subframes. Meanwhile, the UL/DL config#2 102 consists of 6 DL subframes (D), 2 special subframes (S), and 2 UL subframes (U). Among the three UL/DL configurations, the UL/DL conf#2 having the largest number of DL subframes is regarded as the DL heaviest configuration 103.
In the case of performing the traffic adaptation by applying the three configurations 100, 101, and 102 dynamically, there is a need of determining uplink transmission timing of Hybrid Automatic Repeat Request (HARQ) ACK/NACK corresponding to downlink data. In the example of FIG. 1, it is assumed to comply with the HARQ ACK/NACK UL transmission timing of the configuration 102. This is because the configuration 102 has the least number of UL subframes among the three configurations and thus the other two configurations are likely to have the UL timings at the same uplink subframes as the configuration 102, thereby avoiding a problem in that the UL subframe for transmitting the HARQ ACK/NACK is changed to DL subframe in the traffic adaptation process.
In LTE TDD, the HARQ ACK/NACK corresponding to DL data is transmitted at the UL subframe at least after 4 subframes since the transmission timing of the DL data. Accordingly, when complying with the HARQ ACK/NACK transmission timing of the configuration 102, the HARQ ACK/NACK corresponding to the DL data transmitted in the time duration 104 is transmitted at the UL subframe (U) 105.
At the UL subframe 105, the HARQ ACK/NACK is transmitted on the Physical Uplink Control Channel (PUCCH). In this case, the frequency resource of the PUCCH is extended from the edge frequency region to the center direction of the UL system bandwidth as the required PUCCH resource amount increases. When the traffic adaptation is performed dynamically, the PUCCH HARQ ACK/NACK resource is configured under the assumption with the assumption of the DL heaviest configuration 103; however, if non-DL heaviest configuration is applied, the PUCCH resource region is configured larger than required, resulting in resource waste.
In the example of FIG. 1, it is assumed that efficient resource utilization is pursued by changing the PUCCH HARQ ACK/NACK resource amount dynamically according to the UL/DL configuration. The PUCCH resource regions for transmitting the HARQ ACK/NACK corresponding to the DL data transmitted at the special subframe (S) and the DL subframe (D) proceeding the special subframe (S) are denoted by reference numbers 06 and 107. As shown in FIG. 1, the regions 106 and 107 are the frequency regions arranged in sequence from the edge of the uplink system bandwidth. The two subframes are shared in common among the configurations 110, 101, and 102 so as to be present always in the traffic adaptation process. Accordingly, the PUCCH HARQ ACK/NACK resource corresponding thereto is also present always in the traffic adaptation process as configured at the beginning of the PUCCH resource.
However, the DL subframe (D) located two subframes before the special subframe (S) present only in the configurations 101 and 102. Since the DL subframe which is not present in the configuration 100 is added, the number of DL data channels supported in the configurations 101 and 102 increases as compared to the configuration 100. Accordingly, the PUCCH HARQ ACK transmission resource region has to increase as much as the increased DL data channel amount. Here, the increased PUCCH HARQ ACK/NACK resource region is denoted by reference number 108. The PUCCH resource region increased due to the DL subframe (D) is configures at part more inside than the original PUCCH regions 107 and 107. Finally, the DL subframe (D) located three subframes before the special subframe (S) is present only in the configuration 102. The PUCCH HARQ ACK/NACK resource region which is added due to this DL subframe is denoted by reference number 109. Since the PUCCH resource region corresponding to the this DL subframe (D) is configured in addition to the regions 106, 107, and 108, it is located at most inside part of the PUCCH region. Finally, a Physical Uplink Shared Channel (PUSCH) 110 for UL data transmission is present between the PUCCH regions.
On the UL resource for transmitting the PUCCH HARQ ACK/NACK, the Sounding Reference Signal (SRS) for UL band channel estimation is transmitted as well as PUSCH. The base station performs frequency-selective scheduling, power control, and timing estimation based on the channel state information acquired based on the SRS transmitted by each terminal. The SRS is generated based on the Zadoff-chu sequence, and the SRS resource per terminal is split into frequency location including comb and cyclic shift of the Zadoff-chu sequence. Here, the comb is SRS transmission resource split into even-numbered subcarrier (comb 0) and odd-numbered subcarriers (comb 1). The SRS is transmitted at the subframe configured for SRS transmission at the last symbol in the time domain.